Jaws revisited

TRANSCRIPT

NARRATIONGreat white sharks are one of the most graceful and majestic of all the sharks in the ocean. They're also one of the all-time predators.

Ruben MeermanSharks have truly impressive teeth. Like these from a great white. Until recently, scientists have relied on the shape of shark teeth to figure out what they eat. Small prey or large. Now, they're starting to learn more from the jaws.

Dr Steve WroeSharks have very interesting and very different jaws to us. We know surprisingly little about their actual killing and feeding behaviour. They're also, obviously, a very difficult animal to get data from in the wild.

NARRATIONBrave, but no fool, Steve Wroe's work on the bite force of the great white has been based in the lab. Using a real head as his mannequin, Steve's built a sophisticated 3-D computer model of the great white's jaws to determine just how hard it bites.

Dr Steve WroeWe take the head, we put it through a CT scanner, and that took over 400 individual X-ray slices. We segment out the structures of interest. In this case, the jaws, in particular. And then we can take that and build an engineering model, in a separate programme. That model allows us to apply forces and loads, but it also allows us to input the material properties of the shark jaws, themselves. What we found was that for the very largest of white sharks, they were probably biting as hard as anything else alive today. The actual value that I predicted was up to about 1.8 tonnes. And that's a lot of force.

NARRATIONSteve Wroe's PhD student, Toni Ferrara, has taken this research one step further. Using the same engineering modelling as Steve, she's looked at how the great white's jaws handle the massive prey they eat.

Toni FerraraThese colours here show patterns of stress in the jaws. All the way from these cold blue colours where the stresses are low, to these red-hot areas where the stresses are high. These are jaws of the great white with its mouth wide open. You can see the jaws here lit up like a Christmas tree. They're under very high stress.

Ruben MeermanDid you expect to see this much stress?

Toni FerraraNo, we didn't, actually, because the specimen we used is actually a juvenile. So, what happens in great whites, as this animal ages, it's going to add layers of this outer cartilage which'll effectively reinforce the jaws and make them stronger. Even though we knew these jaws aren't fully developed when these sharks are young, we hadn't made the connection these animals need to reinforce their jaws before they'll be able to feed on large prey.

NARRATIONToni's research may offer a new explanation as to why great whites sometimes take a bite out of us.

Dr Vic PeddemorsI think what's really interesting about Toni's work is that we've always wondered why, when sharks bite people here on the east coast of Australia, they tend to just have a single bite and then let go. And, normally, the person is spat out. And that suggests that, in fact, the shark is testing to see if something's edible and now links to the fact that maybe the jaws aren't strong enough to deal with the larger prey. So it really is at that sort of teenager stage where you're testing everything you can and sometimes you get your fingers burnt. To me, the more we know about the mechanisms of biting and feeding, the more we can eventually protect the sharks and, of course, protect humans, along the way.